Volvo: trans/drivetrain clunck, volvo v70 awd, 1999 volvo v70

Question
QUESTION: I have a 1999 Volvo V70 AWD Cross Country automatic with 120K.  I just noticed in the trans or rear drive train there is clunk sound and feeling when I moderately accelerate at speeds between 55 and 70 mph. Not sure if it is related but there has been a humming sound from the rear while on the highway.  It does not seem to be clunking as it is shifting to the next gear. I thought by replacing the tires that it would go away (humming) but it has not.

Thanks

ANSWER: George,
Many faults with the C/C's drive train. Drive shafts, the coupler at the rear axle, the final drive unit. Last one I did was the coupler. I was listening to the wheels and driveshaft as I had the car up in the air, as things were spinning I heard the coupler make noise. Take your car in to a shop that works on the Volvo's and see what they find. Have the shop also look at all the motor/trans mounts making sure all are good and tight. With all the moving parts on the AWD it takes time to find the worn one(s).

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QUESTION: Someone suggested that it maybe the transmission fluid.  I am going to do this as well with the mileage being 120k.  Should I drain and fill or flush?  I have read that the Toyota Transmission fluid is the same as Volvo - WS 3309 automatic gearbox fluid 16 liters is this correct? Or would you recommend another ATF?  Also notice most people put in an additive Lube.  Best place to purchase?

Thanks

Answer
George,
It really should have been done 60k miles ago hopefully to keep the fluid up and trans clean. Check your owners manual some CC's use a synthetic fluid. You could also look at the trans dip stick it may have a marking on it for fluid type. You need to be sure that the fluid you use is correct. I know nothing of the Toyota fluid, sorry. You could just go ahead and use synthetic and you would be all right. I use a BG product that is bought directly from the local BG distributor. A good parts store will have the fluid you need. I would flush the entire trans with the flush machine that will hook up to the cooler line.